If it is a serpentine belt, the tension is automatically adjusted by the tension idler. If the belt is loose then the tensioner needs replacing. If it is a normal drive belt, then the alternator is mounted on a slotted bracket that allows you to adjust the position of the alternator. You can loosen the bolts and adjust the tension on the belt.
You have to install a new belt tensioner.
Loosen alternator remove old belt. Reroute new belt, tighten alternator.
Loosen the tensioner bolt on your alternator. Slide the alternator to the left. Remove the alternator belt. Put the new alternator belt on and tighten the tensioner bolt.
You will need to loosen the alternator belt with the tensioner pulley. When the tensioner pulley is loose the alternator belt will become loose. Put the new alternator belt on and tighten the tensioner pulley.
It should be self adjusting, if it is slipping it could mean you need a new belt or a new belt tensioner.
Disconnect the battery Remove the engine covers to access the alternator drive belts. Remove the electrical connections from the alternator. Slacken the bolts, remove the belt. Remove bolts, put new alternator on, tighten bolts until you can just move alternator, fit new belt, move alternator so the belt is tight and then tighten bolts to their specified torque.
Remove the bolt on the lower front side and two more bolts on the rear of the alternator. Make sure all nuts are off the bolts. Do not loosen the bolts that hold the alternator together. Remove the belt. Now slide the alternator off the mounting bolts. Slide the new alternator onto the two seating bolts, then hand-tighten them. Then slide the next bolt through the alternator and into the engine block.Slide the new alternator onto the two seating bolts, then hand-tighten them. Then slide the next bolt through the alternator and into the engine block. Now tool-tighten all the bolts to secure the new alternator to the engine block.
Begin by loosening the tensioner pulley on your 1999 Mitsubishi Eclipse. The alternator belt will become loose and can be removed. Put the new alternator belt on and tighten the tensioner pulley.
unloosen the 3 bolts on the alternator and push down on it and the belt will come loose, take the belt off and put new belt over the pulleys and to tighten pull up on the alternator and tighten the bottom bolt first and then check the belt for tightness, when you press on the belt there should be about 1/2 inch play, when you get it set then tighten all the bolts on the alternator and your done.
Disconnect the battery. Loosen the alternator bolts and slide the alternator to loosen the belt. Remove any other belts in front of the bad belt if necessary to get to it. Remove the alternator belt, and install the new one. Pull the alternator to the side to tighten the new belt snug and hold while tightening the bolts. Reconnect the battery
What belt? Drive belt is easy, just loose the 3 bolts on the alternator, pry the alternator forward, put the new belt on, pry the alternator back, and tighten the bolts. Power steering belt is much more difficult.
This was hard to do on my 86 2.5L 4 cylinder because in order to put the new alternator belt on... you have to get the other belt off... first what you have to do is loosen up the 2 pivot bolts on the AC compressor from underneath the car.. mine were pretty stubborn but i eventually got em to budge... once you can move the AC, remove the crank/water pump/AC belt. then loosen up the alternator pivot bolt located on the underside of the alternator...(this can be done from either top or bottom) once you can move the alternator.. slip the belt onto the alternator pulley and around the water pump and crank. then tighten the alternator pivot bolts while putting as much possible tension onto the belt and re-tighten alternator into place. then put or replace crank/water pump/AC belt and re-tighten the AC while putting as much possible tension on the belt by pushing the AC forward with a pry bar or screwdriver. good luck